The present invention is directed to a strip for use in construction and repair of surfaces made from drywall. Drywall, which is sometimes referred to as wallboard, is a gypsum-based sheet with heavy paper on the outside surfaces thereof. Drywall is a very common construction material used primarily on interior walls and, sometimes, ceilings. The drywall sheets generally come in panels which are 4 feetxc3x978 feet. As such, it is necessary to form various joints at the edges of the panels. Such joints typically include butt joints where panels lying in the same plane abutt one another, and 90 degree corner joints, both internal and external. Where such joints occur, an installer will typically use paper tape or corner bead as needed.
The prior art includes a wide variety of corner bead and paper tape products. For example, U.S. Pat. No. 5,037,686, and related patents, shows various versions of a drywall tape which is made of plastic and which is suggested for use at various angled and non-angled joints. Another patent to the same inventor, U.S. Pat. No. 4,418,027 shows an improved PVC (polyvinylchloride tape) in which the ability of the PVC strip to adhere to taping compound is enhanced by gluing cotton or synthetic fibers to the surface of the PVC tape. The use of glue to attach a floc as is shown and suggested in the ""027 patent is expensive and difficult, which makes the end product, a product sold under the trademark STRAITFLEX by Con-Form International, Inc., expensive. Because it is itself a laminated product, a drywall strip with floc glued to it to enhance the adhesion of drywall compound to the strip are subject to delamination, particularly when drywall compound, as opposed to a mechanical method such as nailing or stapling, is used to connect the strip to a piece of drywall. Other examples of prior art devices used at the joints of drywall include the products of vinyl corporation in Miami, Fla. Such products are shown, for example, in U.S. Pat. Nos. 5,138,810 and 5,003,743. These products are extruded vinyl forms which are not intended to be flexible enough to ship in a flattened and rolled form.
Yet another example of a prior art device for use in forming joints in drywall construction is shown in U.S. Pat. Nos. 4,977,718 and 4,835,925, which are patents of the Assignee of this invention. These patents show a perforated vinyl strip with a central hinge allowing the strip to be shipped as a roll and formed into a 90 degree angle on site by a drywall installer. While the ""718 patent suggests that the strip may be formed of a polypropylene polymer, vinyl is indicated as the preferred material used to form the strip. Polypropylene, however, is a material to which drywall compound and other construction adhesives do not adhere well. It is of utmost importance that gypsum-based drywall compound, which is used to form and finish joints in drywall construction, adhere well to the strip which is used to bridge the joint either in a butt joint or a corner joint.
The prior art also includes products of the company called Trim-tex, Inc., of Lincolnwood, Ill. U.S. Pat. Nos. 5,752,353 and 5,313,755 show examples of some of the products of Trim-tex, one of which is sold under the name MAGIC CORNER, which is also a vinyl material which includes a corner bead made of two apparently co-extruded materials, a soft flexible PVC in the center and a more rigid PVC at the outer edges. Further information regarding the Trim-tex products can be seen at the web site of Trim-Tex, which is at www.trim-tex.com.
Finally, perhaps the most common device used in drywall construction is a simple galvanized corner bead. The galvanized steel material is preformed into a 90 degree angled shape and generally has perforations. While in common use, the galvanized corner bead suffers from the same difficulty as does the extruded 90 degree angle PVC corner bead, in that they both are bulky and difficult to transport by virtue of the fact that they are preformed into a 90 degree angle shape at the factory.
The present invention allows the manufacture of a low-cost, yet highly effective device for use in forming joints in drywall construction. A mineral filled polypropylene material, which may be extruded into sheet form of very wide widths or into individual strips, is embossed with a simple crease down the center of the strip. The crease may be formed by squeezing the center of the strip between rollers, one of which rollers has narrow protrusion and another has a groove, with the protrusion and groove being aligned. Along with the formation of the crease, the strip is perforated and knurled to increase the surface area and to facilitate the ability of construction adhesives and drywall compound to adhere to the surface of the strip. By using mineral fill instead of plain polypropylene, the strip of the present invention has excellent adhesive characteristics, i.e. drywall compound, printing inks and construction adhesives in general adhere very well to it. Further, in accordance with the invention, an adhesive, preferably applied by spraying, is used to first attach the strip to the drywall sheets being joined. An adhesive particularly suited for use in bonding to polypropylene enables the strip to be firmly fixed to the drywall. Once the strip has been properly positioned, a drywall finisher can then apply drywall compound the finish the joint. The perforations and knurling of the strip of the present invention permit the forming of an excellent bond between the strip and the drywall compound. As used herein, the term xe2x80x9cadhesivesxe2x80x9d is intended to include sprayed adhesives, adhesives dispensed from a tube with a caulking gun, and drywall compound in pre-mixed or dry form.